1. Field of the Invention
This invention relates generally to a method for mitigating park disengagement clunk in an automatic transmission for a motor vehicle.
2. Description of the Prior Art
Disengagement of the park system in automatic transmission vehicles can result in objectionable audible and tactile disturbance to the driver if the vehicle is parked on a grade or up against a curb, such that the park system is maintaining a significant amount of stored strain energy in the vehicle's driveline. This disturbance is called “clunk.” The objectionable disturbance comes from the nearly instantaneous release of this energy when park is disengaged.
Reliance on the use of clutches to ground the transmission output shaft but not the transmission input prior to park disengagement are deficient in transmissions having a kinematic assembly that prevents the output from being grounded with the input free through clutch application.
This deficiency results in a tactile disturbance to the driver when the transmission is grounded or tied-up because torque is transmitted from input to output during this process.